1. Field of the Invention
The present invention is directed to a method and apparatus for detecting the presence of ion exchange resins in a fluid and measuring their concentration. More particularly, the present invention is directed to a test device using a laser light to cause the resin fragments to fluoresce and using their fluorescence to measure the concentration of resin in relatively pure water.
2. The Prior Art
Many industrial and commercial systems require extremely pure water. For example, the art of manufacturing integrated circuits and microprocessors requires that silicon wafers be carefully and thoroughly washed with very pure water between etchings and other manufacturing steps. More particularly, in electrical power generation, boiler feedwater must be very pure or minerals and salts in the water will be deposited throughout the system, reducing its efficiency and shortening its life. In these and other applications, the water used is often treated with ion exchange resins in resin beds to remove impurities. Make-up demineralizers and condensate polisher systems, which are used to purify feedwater, however, leak ion exchange resin fragments into the condensate and feedwater systems during operation. These ion exchange resin fragments are a potential source of impurities such as sulfur, organic chemicals and so forth, and these resins can readily decompose into quite corrosive and reactive organic acids in the boiler system, causing increased corrosion.
In a power plant system, condensate from the turbine is collected in a condenser having a hot well before being pumped back into the system. From the hot well it may be pumped through ion exchange resin beds to remove particulate matter and soluble matter that were introduced from the system or with the makeup water. Leakage of resin fragments occurs during steady state operation and increases substantially during flow transients. For example, when a new bed is put into use increased agitation results in greater leakage of resin into the system. The quantity of leakage varies according to operational variables of the particular system. In a boiler, there are two practical methods of controlling the level of resin contamination in the boiler water. They are generally used together. First, the rate of leakage can be related to the specific details of operation of the boiler and the resin beds. By manipulating these variables over time through gained experience, the level of leakage can be reduced. Second, the blow-down of the system can be increased to remove contaminants faster. Most contaminants are not soluble in steam, so they collect in the water in the boiler. Conventionally, a portion of this water, for example, 0.1%, is continuously removed from the boiler and discarded. Were this not done, the boiler would eventually become filled with sludge. Effective use of both of these methods requires that the level of contaminants is known. The present invention focuses on the level of ion exchange resin fragments in the water, rather than other contaminants.
The prior art includes two methods of measuring the level of ion exchange resin fragments in the boiler water. In the first method, a membrane filter collects resin fragments from a sample of water. The filter is transferred to a specially modified centrifuge tube where an organic solvent dissolves the membrane filter. The filtrate is spun in the centrifuge tube which drives particulate matter into the precision bore stem of the centrifuge tube. The column height of the material is measured, permitting calculation of the volume of the material. The same analysis is preformed on a resin standard of known weight to obtain an apparent density. The weight of the sample is estimated therefrom. This method is extremely labor intensive. It requires filtering a large sample of water on the order of tens or hundreds of liters because the test checks for concentrations in parts per billion. The test is extremely time consuming, requiring several hours of analysis time, leading to stale information. The method also requires special laboratory equipment not commonly available at power stations or other boiler installations. Finally, occasionally interference from other particles, such as iron oxides and colloidal silica and from the membrane filter itself, is encountered.
A second method involves treating the membrane filter with cationic and anionic radiotracers and taking a reading from the sample on a gamma spectrometer. These readings are then compared with readings taken from known standards and the amount of resin fragments is estimated. This method is also very labor intensive and requires sampling tens or hundreds of liters of water. It also takes several hours to perform, reducing the usefulness of the then stale information. The method requires special laboratory equipment not commonly available at power stations or other boiler installations.
These substantial shortcomings in the methods of the prior art have resulted in only sporadic use of condensate polisher systems in boilers. Consequently, a clear need exists for a method and apparatus for conveniently, quickly and inexpensively monitoring and measuring the level of resin fragments in water.